The present invention relates to an ink container for an ink jet print head, comprising a main ink tank, a feed chamber intermediate between the main tank and the head, and a feed channel connecting the main tank with the feed chamber.
The ink container may be of the type which is separable from the print head, in the form of a replaceable cartridge, or else of the type which is fixed to the print head. The print head may, for example, be of the type in which the ink drops are expelled through nozzles by the rapid heating of the ink inside cells communicating with the nozzles.
In the following description, reference will be made by way of example to the case of a container which is fixed to the head, though it should be understood that the invention is applicable to other types of ink container whether fixed or not fixed to the print head.
U.S. Pat. No. 4,831,389 discloses an ink jet print head fixed to its own ink tank and mounted on a moveable carriage of a printer. The tank is filled with a porous ink-soaked foam body. In order to supply the porous foam with fresh supplies of ink to replace that consumed in the course of printing, a sharp hollow needle is passed into the foam body through the tank wall. The needle is connected via a capillary tube to a large-capacity container located in a fixed position at a distance from the head. From here the ink is conveyed to the foam body by capillary action.
The capillary tube, in itself a very delicate component, may be damaged by the continual flexing to which it is subjected by the back and forth movements of the carriage on which the print head is mounted. Moreover if pigmented inks are used, the capillary tube may become blocked by deposits of pigments when the printer is out of use for long periods.
Also known is a method of manually refilling the tank of an ink jet print head, for example that described in U.S. Pat. No. 4,929,969, in which the tank fixed to the print head is packed with a foam body impregnated during manufacture with a predetermined amount of ink.
In order to avoid throwing away the tank/head unit when the ink is exhausted, a refill device described in Italian Utility Model Application No. TO91U 000234 can be used. This consists of a flexible container containing the ink and having a thin tube which is introduced into the empty tank through an aperture in its cover. By manually compressing the flexible container, a certain amount of ink is introduced into the foam body of the print head.
This method of refilling is complicated and hazardous because the insertion of the refilling tube into the foam body may damage its capillary structure, reducing its ability to maintain the pressure drop needed for a correct supply to be maintained to the head. The violent injection of a squirt of ink may create air bubbles in the foam body which remain trapped in the pores and in the capillary channels of the foam body, affecting the best pressure drop values. Furthermore there is always the possibility that the ink may leak and get over the operator or surrounding objects.